Liquid Crystal Displays (LCDs) contain several layers which work in combination to create a viewable image. A backlight is used to generate the rays of light that pass through what is commonly referred to as the LCD stack, which typically contains several layers that perform either basic or enhanced functions. The most fundamental layer within the LCD stack is the liquid crystal material, which may be actively configured in response to an applied voltage in order to pass or block a certain amount of light which is originating from the backlight. The layer of liquid crystal material is divided into many small regions which are typically referred to as pixels. For full-color displays these pixels are further divided into independently-controllable regions of red, green and blue subpixels, where the red subpixel has a red color filter, blue subpixel has a blue color filter, and green subpixel has a green color filter.
The light which is passing through each subpixel typically originates as “white” (or broadband) light from the backlight, although in general this light is far from being uniform across the visible spectrum. The subpixel color filters allow each subpixel to transmit a certain amount of each color (red, green or blue). When viewed from a distance, the three subpixels appear as one composite pixel and by electrically controlling the amount of light which passes through each subpixel, the composite pixel can produce a very wide range of different colors due to the effective mixing of light from the red, green, and blue subpixels.
Currently, the common illumination source for LCD backlight assemblies or Back Light Unit (BLU) is fluorescent tubes, but the industry is moving toward light emitting diodes (LEDs). Environmental concerns, small space requirements, lower energy consumption, and long lifetime are some of the reasons that the LCD industry is beginning the widespread usage of LEDs for backlights.
LCDs are becoming popular for not only home entertainment purposes, but are now being used as informational/advertising displays in both indoor and outdoor locations. When used for information/advertising purposes, the displays may remain ‘on’ for extended periods of time and thus would see much more use than a traditional home theatre use. Further, when displays are used in areas where the ambient light level is fairly high (especially outdoors or in aircraft cockpits) the displays must be very bright in order to maintain adequate picture brightness. When used for extended periods of time and/or outdoors, durability of the components especially the illumination sources such as LEDs can become an issue.
As is readily apparent, an LCD will not function satisfactorily without an appropriate backlight system. The backlight is essential for proper functioning as the image or data displayed on the liquid crystal layer may only be viewed while the backlight is providing proper illumination to the liquid crystal stack. If the backlight system should fail completely or operate at a less than optimal level, then the LCD will not perform satisfactorily. While this may be a simple inconvenience when LCDs are used for entertainment purposes, when used for information or data displays this can be very costly. For example, LCDs are now being used in cockpits of aircraft as well as the instrument panels or display in ground vehicles and marine equipment. In these applications, when there is a failure of the backlight, the LCD may no longer display the important information for the vehicle/aircraft and controls may cease to operate. These situations can be undesirable not only to the passengers of the vehicle/aircraft, but also other soldiers who are counting on this part of the mission.
LEDs, however, have a limited life span, and eventually their luminance will degrade until little or no luminance is generated. Some LEDs may quickly fail simply due to a manufacturing defect or may fail due to shock/forces applied to the aircraft or ground vehicle. Currently when this occurs in an LED backlight, the entire backlight assembly must be manually replaced (i.e., the element which every LED is mounted to is replaced with a new element containing all new LEDs). This is expensive, and is often time consuming. Alternatively, the LED backlight assembly could be removed from the display housing, and the degraded or faulty LEDs could be manually replaced. This is typically even more costly, and involves extensive manual labor. In currently known units, this also requires virtual complete disassembly of the LCD to gain access to the backlight. This complete disassembly is not only labor intensive, but must be performed in a clean room environment and involves the handling of expensive, delicate, and fragile components that can be easily damaged or destroyed, even with the use of expensive specialized tools, equipment, fixtures, and facilities.
Thus, there exists a need for a more durable and dependable backlight for a LCD so that failures can be accounted for and vehicles/aircraft can complete a mission and/or return safely to base.